The document summarizes an experiment on failure analysis of brittle and ductile materials under impact and tensile loading. In impact testing, brittle materials like window glass and tile shattered into the most fragments when dropped, while the ductile polycarbonate did not crack. In tensile testing, aluminum foil stretched the most and was concluded to be the most ductile material, followed by brass, with copper being the stiffest. The experiments supported that ductile materials absorb applied forces rather than releasing them as new surface area like brittle materials.

1. Failure Analysis of Brittle and Ductile Materials: Raising the Surface Energy 2007 North Carolina State Science Fair ______ Middle School 6th Grade Entry by _____Deleted for privacy purposes_____ Science Instructor: Ms. __________ February 13, 2007

2. Table of Contents Background Motivation Problem Hypothesis Material Lists Experimental Procedures and Variables Results Observations and Data Analysis Conclusions Acknowledgements

3. Background Structure is a long molecular chain Actually a type of plastic although clear like glass Material is light but very durable Can be laminated to make “ bullet resistant glass” Crystal structure of silica or quartz or “glass” Hard, but easily broken due to symmetry of crystal and microscopic defects Most common particle found in sand

4. Background Many ductile materials are metals that have an FCC crystal structure including Aluminum and Copper Brass is a substitutional alloy of copper and zinc

5. Motivation  Failure Analysis Can . . . . Improve human safety Prevent plane crashes Bullet resistant shielding Improve engineering design Cars (safety features) Trains Sky Scrapers Help criminal investigations Forced entry Improve environmental protection Prevent oil tanker spills Video deleted for privacy purposes Figure containing sensitive (military) information not shown

6. Problem and Hypothesis Problem : How and which materials fail under the conditions of impact force and/or tensile loading and how is energy transferred to these materials under these conditions? Hypothesis: Under impact testing (window glass, tile, acrylic glass, polycarbonate), all the brittle materials will shatter or break into fragments. The window glass will break into the most fragments. Under ductile testing (Aluminum, Brass, Copper) the metal sheets will bend and the aluminum foil will probably tear completely. The most ductile metal will be the copper.

7. Impact Testing Materials Brittle Targets: Window glass Acrylic glass Bathroom tile Polycarbonate Impact Forces: Large chrome doorknob Brass Caster Support Materials: Large cardboard box Large wooden box Large foam pillow Tape measurer or ruler Glass cutting kit Saftey goggles Leather gloves 5lb Postal scale Ziplock plastic bags Optional: Digital camera

8. Impact Testing Procedure Put on saftey goggles and leather gloves Cut pieces of target material to be 11 X 11cm except for polycarbonate or acrylic glass, for these mark an area of the same dimensions on the material with a marker Place target material on support material and setup testing area to prevent injury. Weigh each impact force material with the postal scale Drop impact force material onto the target from exactly 3 ft by using the tape measure Optional : Before touching anything take a picture of broken pieces or damages from targets using the ruler or tape measure as a scale in the picture Carefully count the number of pieces and record the data before storing them in the Ziplock bags. Impact Energy Effects : Repeat procedure using the brass caster or another spherical-like object of different weight. Using the weight value to calculate the potential energy or impact energy. Support Material Effects : Repeat procedure using the different support materials

9. Impact Testing

10. Tension Testing Materials Tensile Specimen Aluminum foil Copper flashing Brass sheet Scissors Two C-clamps 1 gallon jug 10lb postal scale Safety goggles and leather gloves Level or large ruler Caliper

11. Tension Testing Procedure Cut out ~0.1 mm thick, 16X6 inch metal strips from the tension specimen using scissors. Measure thickness with Caliper. Five sheets of standard Al foil pressed together should equal a 0.1mm thickness. Find two flat parallel bars suspended in air or line up two table overhangs of equal height separated by a known distance. Use these surfaces to firmly clamp down the metal strips on both ends with the length of the strip suspended in air between the two clamps Mark the center of the metal strip (half the length) with a line at one of the edges to indicate the measuring point. Weigh the jug on the postal scale Measure the height of the metal strip with the level/ruler from the measuring point to the floor. Place the empty jug in the center of the metal strip and measure the height again at the measuring point. Effect of Loading : Take off the jug and repeat steps 4), 5), and 6) but while increasing the weight of jug by filling with various levels of water (make sure to close the jug tightly). Calculations: Use the change in height plus some geometry to find the change in length of the tension specimen. The length during the load minus the length after load is the change in the elastic deformation length. The length after load minus the length before the load is the change in the plastic deformation length.

12. Tension Testing

13. Impact Testing Results Cracks Fragments Cracks Fragments

14. Impact Testing Observations / Data Analysis More Brittle = More Fragments Window glass is very brittle Both Impact Energies not enough to break Acrylic glass or polycarbonate Polycarbonate so ductile it doesn’t crack!! Foam support adsorbs a lot of impact energy (Foam support actually broke) so there is less energy to directly break the target, however the time of impact is longer. Wood adsorbed the least impact energy so the time of impact was shorter. Impact of tile on wood support caused many small pieces in specific area because of nail underneath, caused error in data Cardboard adsorbs a little less energy than foam and allows for an impact time longer than that for wood. This caused a larger # of fragments for the window glass

15. Forms of Energy during Impact Testing Before dropping, impact force there is a certain potential energy. During drop, potential energy changes into kinetic energy After impact, energy is either adsorbed as strain energy or released as new surface energy More surface energy = more surface area = more pieces

16. Tension Test Results

17. Tension Testing Observations / Data Analysis Copper had cardboard backing which may have introduced some errors in our results, esp. for the elastic deformation b/c the cardboard seemed to make it more elastic General trend – Aluminum is the most ductile, then Brass, then Copper consistent with published results

18. Conclusions Impact Testing Conclusions: More surface energy = more surface area = more fragments. Window glass and tile are the most brittle since they adsorb less impact energy but instead release surface energy so more fragments are created under impact forces. Polycarbonate is the least brittle (actually ductile) as it adsorbed more impact energy without releasing surface energy so it didn’t even have cracks. Tensile Testing Conclusions: Copper was not the most ductile but was actually the most stiff as it had highest elastic modulus, so my hypothesis was wrong. Alloying copper and zinc (brass) allows it to become more ductile than either copper or zinc. Aluminum is most ductile since it had the lowest elastic modulus and did not tear under the applied load. Energy from tensile load is adsorbed by ductile materials and stretches elastically or plastically instead of rapidly breaking it into pieces.

19. Acknowledgments I want to thank . . . . Deleted for privacy purposes